Take a game like Undertale: whenever a character "talks", the text is printed out one by one, and a sound is played for each letter, as if the character is actually talking (even if it's just gibberish). These sounds are usually different for each character. What are those types of sounds called? If I wanted to get placeholder sounds for such a dialog system, how do I find them?
Voice acting is ubiquitous in video games today, but in the old days, when budgets were smaller, sound hardware was more basic, and disk/cartridge space was limited, developers had to resort to text. In games where story was emphasized, they figured some of the drama was lost when a potentially emotional scene was pantomimed like a silent movie. So some games incorporated "sort of" voice acting, in two forms.
One form is a sort of beeps at various pitches, generally speeding up or slowing down depending on how quickly the speaker is talking. ...
Or, when the sounds are nonsense syllables rather than beeps & typing, Speaking Simlish:
The language of NPCs and other AI constructs in simulation games and some RPGs, made up of nonsense sounds strung together like actual words. It's not a cypher, normal speech spoken backwards or anything like that, it is quite simply gibberish or "Simlish" as the Sims Manual says
This became especially popular in cartridge and floppy-based releases once fully voiced CD-ROM releases began showing up, as something of a compromise between the expression provided by voice acting and the enormous amount of storage required for it
Something like the voices in Banjo Kazooie could be considered either of the above, I'd say.
There's no specific word to describe this particular effect. On the other hand, we can think of printing words letter by letter and playing a sound for each letter written as a typewriter-like animation. This said, you may call those sounds just 'typewriter typing' or similar.
If you had some sound resources in a project, you could name them 'sndTextTyping1', 'sndTextTyping2'...
If you don't want to rely on those terms and want to know the exact word (in case it actually exists), you may want to ask this question on the English Language & Usage Stack Exchange site.
In addition to the other answers, this 'grunting' is used to simplify game localization. This way the developers don't have to hire voice actors in every supported language, and manage those different recordings per region.
To replicate this effect, you could record various random 'syllables' in each voice (10 samples might do). Manually store the number of syllables for each text word in your dialog. Then play a random 'grunt' sound for each syllable in each dialog word. You could fudge it and just play random grunts regardless of the actual number of syllables.